The obesity epidemic is associated with excessive intake of calorie dense, palatable foods and fluids. Oral and postoral chemical signals are integrated in the central nervous system to adjust food and fluid selection, control meal size, and establish taste preferences. Yet little is known about precisely how these signals are integrated to change intake behavior. Progress has been hampered by the lack of available sensitive techniques that probe postoral chemosensory signals and link those to intake behaviors. Recently, chemoreceptors and associated signaling molecules involved in taste transduction (e.g., T1Rs, T2Rs, -gustducin) have been discovered in postoral GI cells, suggesting the interesting possibility that taste properties are among the information encoded in ascending postoral signals and may directly access and impact matching chemosensory signals arising from the oral cavity. Considering oral and postoral sensory signals ascend the central nervous system in roughly parallel pathways, it is especially surprising then that very little experimental attention has been paid to direct influence of postoral signals on primary taste sensory processing. As such, the presence of a common sensory system provides a framework for probing chemospecific influences of postoral signals on well characterized taste-guided behaviors. The present proposal seeks support to begin the psychophysical assessment of chemospecific influences of postoral signals on taste responsiveness in a rat model. Two taste-specific, and complementary, behavioral techniques will be used to assess the effects of intraduodenal chemical infusions on (a) hedonic evaluation of and (b) sensitivity to, independent of the hedonic valence of the stimulus, an oral taste stimulus. Specific Aim 1 tests the hypothesis that postgastric signals influence the hedonic evaluation of an oral taste stimulus in a chemospecific manner in the taste reactivity test. Specific Aim 2 tests the hypothesis that postgastric signals influence oral taste sensitivity in a chemospecific manner in the two response operant taste signal detection task. Not only will applying these psychophysical techniques identify novel, and potentially, important types of primary sensory integration, it will afford me training in new behavioral approaches and data analyses (e.g., psychometric functions) and expose me to a new area of conceptual expertise centered on gustatory function. Such psychophysical testing of GI taste signals through their specific impact on oral taste processing will direct future work on the underlying neural mechanisms, with the ultimate goal of identifying potential targets and strategies to augment sensory feedback crucial to the control of food intake.